The present invention relates to internal combustion engines. More specifically, this invention relates to an exhaust system that improves the efficiency of an internal combustion engine and, thus, also reduces emissions therefrom.
Conventional internal combustion engines have proven to be the single most prevalent source of atmospheric pollution. To a very large degree, the pollution results from the need to maximize the power and performance of such engines, which leads to high compression ratios, which in turn result in incomplete combustion processes and the emission of large amounts of gaseous particulate pollutants. In an effort to remedy the emission pollution problems, complex valving arrangements and electronic control circuits have been added to the basic design of the engines. In some respects, emissions have been substantially reduced by such efforts. However, this reduction in emissions has resulted in a substantial increase in engine costs. Further, engine efficiencies have been reduced to an extent. These problems are essentially due to the use of certain environmental control devices, some of which are discussed below.
Heretofore, various combinations of devices have been used to reduce all three major exhaust gas pollutants, i.e., nitrogen oxides (NO.sub.X), hydrocarbons (HC) and carbon monoxides (CO). Generally, exhaust gas recirculation systems (EGRs) have been used to reduce nitrogen oxides while after-treatment devices have been used to reduce hydrocarbons and carbon monoxides.
Exhaust gas recirculation systems generally require the carburetor of the engine to be set slightly richer than the stoichiometric airflow ratio for securing drivability and performance of after-treatment devices. Accordingly, certain operating efficiencies are reduced. Further, these complex devices increase initial engine costs as well as subsequent maintenance costs.
After-treatment devices include air pumps and catalytic converters. Air pumps are used to pump secondary air into the exhaust system in an attempt to improve combustion in the exhaust. However, it has been found that air pumps cause turbulent flow in the exhaust pipes which detracts from optimum combustion and clarification of exhaust gases. It is believed that one reason air pumps cause turbulent flow is that they operate continuously when the exhaust valves are open, as well as when they are closed. When an exhaust valve is open and exhaust discharged therethrough, air forced into the exhaust system by the air pump interferes with the downstream flow of the exhaust and creates turbulence. Turbulence also can be created by forcing secondary air into the exhaust system at excessive pressure. A further disadvantage of air pumps is that they reduce horsepower.
A catalytic converter is a reaction chamber typically containing a finely divided platinum-iridium catalyst into which exhaust gases from an automotive engine are passed, together with excess air, so that carbon monoxide and hydrocarbon pollutants are oxidized to carbon dioxide and water. Among the drawbacks of these catalytic converters is their adverse effect on power. For example, it is desirable to position the thermal reactor near the engine as much as possible to utilize the heat of exhaust gases before that heat gets out, and so usually it is directly connected to the exhaust port. This arrangement brings into effect a loss of desired exhaust gas stream characteristics which in turn causes a loss in power. Another disadvantage of catalytic converters is that sulphur is emitted from the exhaust system once the effective life of the converter has expired. The expiration of the life of the converter generally goes undetected, unless the automobile is subjected to an emissions inspection.
Another known after-treatment device incorporates heat insulators in the exhaust passage to maintain the high temperature exhaust gases at a temperature level whereby combustible contaminants are oxidized without entailing any power loss due to adverse effects on the exhaust gas stream as in the case of using thermal reactors. However, secondary air still is generally needed to provide the requisite oxygen for combustion in the exhaust system. This usually entails the use of pumps and accompanying apparatus that not only increase the cost of the automobile, but are subject to maintenance and repair, and possibly replacement, as well as the problems discussed above.
Accordingly, there has been a need for a novel exhaust system that avoids the problems and disadvantages of the prior art. Such an exhaust system should provide that combustion of exhaust gases flowing therethrough is uninhibited and combustion of unburned gases occurs to the extent that the concentration of harmful emissions exiting from the tail pipe(s) is substantially reduced. Moreover, such a system is needed which may be easily adapted to standard internal combustion engines, requiring little or no modification to the engine itself, other than in connection with the treatment of exhaust gases. The present invention fulfills these needs and provides other related advantages.